Wednesday, September 21, 2011

World's smallest electric motor made from a single molecule

 The smallest electrical motor on the planet, at least according to Guinness World Records, is 200 nanometers. Granted, that's a pretty small motor -- after all, a single strand of human hair is 60,000 nanometers wide -- but that tiny mark is about to be shattered in a big way.

Chemists at Tufts University's School of Arts and Sciences have developed the world's first single molecule electric motor, a development that may potentially create a new class of devices that could be used in applications ranging from medicine to engineering.

In research published online Sept. 4 in Nature Nanotechnology, the Tufts team reports an electric motor that measures a mere 1 nanometer across, groundbreaking work considering that the current world record is a 200 nanometer motor. A single strand of human hair is about 60,000 nanometers wide.

According to E. Charles H. Sykes, Ph.D., associate professor of chemistry at Tufts and senior author on the paper, the team plans to submit the Tufts-built electric motor to Guinness World Records.

"There has been significant progress in the construction of molecular motors powered by light and by chemical reactions, but this is the first time that electrically-driven molecular motors have been demonstrated, despite a few theoretical proposals," says Sykes. "We have been able to show that you can provide electricity to a single molecule and get it to do something that is not just random."

Sykes and his colleagues were able to control a molecular motor with electricity by using a state of the art, low-temperature scanning tunneling microscope (LT-STM), one of about only 100 in the United States. The LT-STM uses electrons instead of light to "see" molecules.

The team used the metal tip on the microscope to provide an electrical charge to a butyl methyl sulfide molecule that had been placed on a conductive copper surface. This sulfur-containing molecule had carbon and hydrogen atoms radiating off to form what looked like two arms, with four carbons on one side and one on the other. These carbon chains were free to rotate around the sulfur-copper bond.

The team determined that by controlling the temperature of the molecule they could directly impact the rotation of the molecule. Temperatures around 5 Kelvin (K), or about minus 450 degrees Fahrenheit (oF), proved to be the ideal to track the motor's motion. At this temperature, the Tufts researchers were able to track all of the rotations of the motor and analyze the data.

While there are foreseeable practical applications with this electric motor, breakthroughs would need to be made in the temperatures at which electric molecular motors operate. The motor spins much faster at higher temperatures, making it difficult to measure and control the rotation of the motor.

"Once we have a better grasp on the temperatures necessary to make these motors function, there could be real-world application in some sensing and medical devices which involve tiny pipes. Friction of the fluid against the pipe walls increases at these small scales, and covering the wall with motors could help drive fluids along," said Sykes. "Coupling molecular motion with electrical signals could also create miniature gears in nanoscale electrical circuits; these gears could be used in miniature delay lines, which are used in devices like cell phones."

The Changing Face of Chemistry

Students from the high school to the doctoral level played an integral role in the complex task of collecting and analyzing the movement of the tiny molecular motors.

"Involvement in this type of research can be an enlightening, and in some cases life changing, experience for students," said Sykes. "If we can get people interested in the sciences earlier, through projects like this, there is a greater chance we can impact the career they choose later in life."

As proof that gaining a scientific footing early can matter, one of the high school students involved in the research, Nikolai Klebanov, went on to enroll at Tufts; he is now a sophomore majoring in chemical engineering.

This work was supported by the National Science Foundation, the Beckman Foundation and the Research Corporation for Scientific Advancement.

Tufts University, located on three Massachusetts campuses in Boston, Medford/Somerville, and Grafton, and in Talloires, France, is recognized among the premier research universities in the United States. Tufts enjoys a global reputation for academic excellence and for the preparation of students as leaders in a wide range of professions. A growing number of innovative teaching and research initiatives span all campuses, and collaboration among the faculty and students in the undergraduate, graduate and professional programs across the university is widely encouraged.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Tufts University.

Journal Reference:

Heather L. Tierney, Colin J. Murphy, April D. Jewell, Ashleigh E. Baber, Erin V. Iski, Harout Y. Khodaverdian, Allister F. McGuire, Nikolai Klebanov, E. Charles H. Sykes. Experimental demonstration of a single-molecule electric motor. Nature Nanotechnology, 2011; DOI: 10.1038/NNANO.2011.142

Physicists capture microscopic origins of thinning and thickening fluids

 In things thick and thin: Cornell physicists explain how fluids -- such as paint or paste -- behave by observing how micron-sized suspended particles dance in real time. Using high-speed microscopy, the scientists unveil how these particles are responding to fluid flows from shear -- a specific way of stirring.

Observations by Xiang Cheng, Cornell post-doctoral researcher in physics and Itai Cohen, Cornell associate professor of physics, are the first to link direct imaging of the particle motions with changes in liquid viscosity.

Combining high-speed 3-D imaging techniques with a sensitive force-measuring device, the researchers tracked the motions of tiny particles suspended in the fluids while monitoring the thinning or thickening behaviors under shear.

They found that fluids become thinner when the particles -- which normally move in a random way -- get swept by the induced fluid flows.

In addition, they showed fluids became thicker or more viscous when particles were driven past one another too quickly for the fluid between them to drain or get out of the way. At such high speeds, the particles form clusters that lock together and make the fluid more viscous.

Grasping the physics of shear thinning and thickening isn't just good for at-home science experiments, knowledge of fluid phenomena are important for commerce. "In industry, understanding the thinning and thickening of materials is crucial for almost any transport process," Cohen said. These findings will improve the ability of scientists and engineers to handle complex fluids ranging from such industrial materials as paints, detergents and pastes, as well as such biological liquids as lymph and blood.

The researchers' observations refute theories that such changes in fluid viscosity result from the formation and destruction of particle layers under shear. The idea behind these theories is that, like lanes on a highway, streamlining particle trajectories reduces random collisions and enables particles to flow past each other more smoothly. When the particles form layers at low shear rates, the viscosity decreases, causing the fluid to thin; when the particle layers break up at high shear rates, the viscosity increases, causing the fluid to thicken.

However, by directly imaging the layering and measuring the fluid viscosity, the Cornell scientists found that while the amount of layering and delayering was comparable, the changes in viscosity were substantially different in the thinning and thickening regimes.

Moreover, the delayering occurred at shear rates much lower than those leading to thickening. Hence, they produced evidence that layering is not the major reason for viscosity changes in these suspensions.

The work was supported by the National Science Foundation, King Abdullah University of Science and Technology and the U.S. Department of Energy.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Cornell University.

Journal Reference:

Xiang Cheng, Jonathan H. Mccoy, Jacob N. Israelachvili, Itai Cohen. Imaging the microscopic structure of shear thinning and thickening colloidal suspensions. Science, 2 September 2011: Vol. 333 no. 6047 pp. 1276-1279 DOI: 10.1126/science.1207032

New insight into how disordered solids deform

 In solid materials with regular atomic structures, figuring out weak points where the material will break under stress is relatively easy. But for disordered solids, like glass or sand, their disordered nature makes such predictions much more daunting tasks.

Now, a collaboration combining a theoretical model with a first-of-its kind experiment has demonstrated a novel method for identifying "soft spots" in such materials. The findings from University of Pennsylvania and Syracuse University physicists may lead to better understanding of the principles that govern materials responses ranging from failure of glasses to earthquakes and avalanches.

The experimental research was conducted by professors Arjun G. Yodh and Andrea J. Liu, along with post-doctoral associates Ke Chen, Wouter G. Ellenbroek and Zexin Zhang and graduate student Peter J. Yunker, all of the Department of Physics and Astronomy in Penn's School of Arts and Sciences. They collaborated with Lisa Manning of the Department of Physics at Syracuse. Liu and Manning described the theoretical model in a separate study.

Both studies appear in the journal Physical Review Letters.

For materials with well ordered, crystalline internal structures, such as diamonds or most metals, identifying soft spots is easy; weak, disordered sections stick out like a sore thumb.

"In perfect crystalline materials, atoms are in well-defined positions. If you give me the position of one atom, I can tell you the position of another with precision," Yodh said. "There's also a well defined theory about what's happening with defects in crystals when stresses are applied to them."

"There's no periodicity in glass, however," Chen said. "You can't look at it and say, 'This part looks different than the rest,' because there is no background pattern to compare it with."

With physical structure a dead end for identifying soft spots, the physicists turned to another property: vibrations. Though the word "solid" is synonymous with "unmoving," the particles that make up solid matter are constantly vibrating. And like the different tones of guitar strings, there are many different ways particles in a solid can vibrate. These are known as "vibration modes."

For crystalline materials, the regular patterns of atoms lead to uniform patterns of vibrations within the material; nearly all particles are involved in a typical vibration. In disordered materials, with their unevenly spaced particles, particles in different regions vibrate differently, producing some new and different vibration modes, particularly at low frequencies.

"We can determine the spatial patterns of the different vibrations in our experiment, and then we can find out whether some of them, particularly low frequency vibrations, are connected with rearrangements or failure of the material when it is stressed," Chen said.

Manning and Liu developed a simulation to test this kind of correlation under idealized conditions. They were able to show that certain regions highlighted by low frequency vibration modes acted like defects in disorganized materials and that these defects were good candidates for where the material would fail when stressed.

"We showed, for the first time, a correlation between the soft spot population and rearrangements under stress," Manning said. "This is something people have been looking for over the past 30 or 40 years."

Though the success of the simulation was an exciting result by itself, it was only a first step. Real-world systems have additional layers of complexity, notably temperature and related thermal fluctuations that can rapidly change the interactions between neighboring particles and thus the system's vibrational patterns.

"It was not at all obvious that the soft spots we found in the simulation would still exist in the presence of thermal fluctuations, which are unavoidable in the real world," Liu said. "Thermal fluctuations, for example, might have caused the soft spots to be wiped out too rapidly to be used for analysis."

To see if this was the case, Chen developed an experimental system with many features similar to the one in the simulation. At its core was a colloidal glass, an effectively two-dimensional material consisting of a single disordered layer of soft plastic particles tightly packed together.

By analyzing video of the particles' motion in the colloidal glass as observed under a microscope, Chen was able to calculate the vibration patterns and then use Manning and Liu's model to locate regions vulnerable to rearrangement once the glass was put under stress. He then compared these regions to the rearrangements that actually happened.

Just as in the simulation, the soft spots predicted candidates for rearrangement, as some of the identified soft spots remained intact while others deformed. The experiment thus provides a new basis -- low frequency vibration modes -- for analyzing real-world disordered solids.

"Low frequency vibrations correspond to areas with weak interaction between particles, and because of these weak interactions their structure is less stable. When they're perturbed there is less resistance from their neighbors." Chen said.

Disordered solids are much more common than ordered ones, so having a working theory of how, why and where they break has many potential applications.

"You can bend a metal spoon, but you can't bend one made out of glass without breaking it. If you can understand how disordered solids fail, you might be able to make them tougher," Yodh said.

The research was funded by the National Science Foundation, including the Penn Materials Research Science and Engineering Center, the Princeton Center for Theoretical Science at Princeton University, NASA and the U.S. Department of Energy.

Zexin Zhang has appointments with the CNRS-Rhodia-UPenn Complex Assemblies of Soft Matter collaboration and the Center for Soft Condensed Matter Physics and Interdisciplinary Research, Soochow University, China.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of Pennsylvania.

Journal References:

Ke Chen, M. Manning, Peter Yunker, Wouter Ellenbroek, Zexin Zhang, Andrea Liu, A. Yodh. Measurement of Correlations between Low-Frequency Vibrational Modes and Particle Rearrangements in Quasi-Two-Dimensional Colloidal Glasses. Physical Review Letters, 2011; 107 (10) DOI: 10.1103/PhysRevLett.107.108301M. Manning, A. Liu. Vibrational Modes Identify Soft Spots in a Sheared Disordered Packing. Physical Review Letters, 2011; 107 (10) DOI: 10.1103/PhysRevLett.107.108302


Neutron analysis reveals unique atom-scale behavior of 'cobalt blue'

 Neutron scattering studies of "cobalt blue," a compound prized by artists for its lustrous blue hue, are revealing unique magnetic characteristics that could answer questions about mysterious properties in other materials.

Experiments at the Spallation Neutron Source (SNS) and High Flux Isotope Reactor (HFIR), both located at the Department of Energy's Oak Ridge National Laboratory, indicate novel behaviors in the antiferromagnetic material cobalt aluminum oxide, -- CoAl2O4, or cobalt aluminate -- which researcher Gregory MacDougall of ORNL's Neutron Scattering Sciences Division describes as a "highly frustrated magnetic system."

"Frustrated" in this context refers to a condition where competing interactions between the magnetic spins within the atomic structure prevent the establishment of a long-range ordered state.

"Frustration is often associated with exotic behavior in materials, including piezoelectricity, multiferrocity, and high-temperature superconductivity, each of which is potentially important for future energy-efficient technologies," MacDougall said.

Antiferromagnetism is a type of magnetic order commonly found in materials below a certain temperature where the microscopic magnetic moments (often called "spins") on neighboring atoms align with their north and south poles oriented in opposite directions. Long-range antiferromagnetic order is technologically important for magnetic information storage.

The single-crystal experiments performed at ORNL showed the magnetic properties of cobalt aluminate exhibited drastic changes at the numbingly low temperature of 6.5 Kelvin. The experiments showed that effects from competing interactions may be responsible for its intriguing but poorly understood magnetic properties.

"Cobalt blue demonstrates behaviors that have never before been appreciated in a frustrated magnet, but have been seen in other materials," MacDougall said.

"Typically, frustration in the lattice from different energy scales and competing interactions drives the ordering temperature down. What we've found is, instead of eliminating ordering entirely, the long-range order is broken up into several small domains, in which the motion of the domain walls is frozen into place," MacDougall said.

Sharp walls separate those smaller atom-scale domains, set apart by the orientation of the atoms' magnetic spin. The result of freezing such walls into place is a glass-like behavior, normally indicative of highly disordered structure.

In cobalt aluminate's case, however, the glass-like behavior is exhibited on a very clean, ordered crystal. "We think this may explain unexpected glass-like behavior in other frustrated systems," MacDougall said.

The research, reported in Proceedings of the National Academy of Sciences, is part of a larger program to study magnetic frustration -- what happens in magnetic systems when the geometry of the system or competing interactions frustrate or suppress the interactions that normally drive order, allowing novel behaviors to emerge.

"This is where you discover new physics," MacDougall said.

Cobalt aluminate is the compound responsible for cobalt blue, a vivid pigment used in paintings, colored glass and even to color concrete.

"In the past seven or eight years people have become interested in cobalt blue's magnetic properties because it turns out to be a prototypical system where competing interactions suppress magnetic order, and it is predicted to have novel ground states," MacDougall said.

The experiments were performed on two of HFIR's Triple Axis Spectrometers and the SNS's Cold Chopper Neutron Spectrometer (CNCS), making use of both thermal and "chilled," low-energy neutrons to study the cobalt aluminate at low, near absolute-zero temperatures. The single-crystal samples were fabricated in collaboration with ORNL's Correlated Electron Materials group.

MacDougall and colleagues used the triple-axis spectrometers at HFIR to study the ordering pattern of the cobalt blue lattice, which revealed the smaller domains forming at low temperatures. With SNS's CNCS, the researchers were able to study how long-lengthscale perturbations in the magnetic ordered states, known as "spin-waves," moved through the system. The speed of those spin waves in different directions is a sensitive measure of the strength of the interactions between atoms in the cobalt blue system.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by DOE/Oak Ridge National Laboratory.

Journal Reference:

Gregory J. MacDougall, Delphine Gout, Jerel L. Zarestky, Georg Ehlers, Andrey Podlesnyak, Michael A. McGuire, David Mandrus, Stephen E. Nagler. Kinetically inhibited order in a diamond-lattice antiferromagnet. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1107861108

Digital microfluidics opening the way for revolution in blood sampling

The days of the blood sample routine - arm out, tie tube, make a fist, find a vein and tap in -- may soon be over, thanks to a new analysis method developed at U of T by Institute of Biomaterials and Biomedical Engineering (IBBME) core professor Aaron Wheelerin which only a pinprick of blood is necessary.

Traditional methods of blood sampling requires intravenous extraction of several millilitres of blood. A phlebotomist then separates serum, which is frozen for transport or storage and later thawed and analyzed. A relatively new alternative to the traditional method uses blood samples stored as dried (DBSs).

The DBS method requires only a pinprick to extract a few microlitres of blood, which is blotted onto filter paper, where the sample, it has been found, remains stable. While DBSs have been gaining increasing popularity for the ease of sampling and storage for some time, they are still not a standard , and the process for using them remained laborious -- until now.

In a study published in Lab on a Chip last week, Wheeler and colleagues demonstrated the proof-of-principle that digital microfluidics could be used to automate the process of dried blood spot analysis in the case of testing for specific genetic diseases at Newborn Screening Ontario (NSO) in Ottawa. This paper is the result of a collaboration between Wheeler and NSO rsearchers.

NSO regularly screens every baby born in Ontario for - some 140 000 babies a year - and collects DBS samples via heelprick. Each DBS must be manually collected. Technicians must prepare the sample for testing, put it into a centrifugal tube, pipette onto the sample, extract the necessary material by , and then use robotics to conduct the chemical analysis.

Wheeler’s digital microfluidic platform automates this process. Droplets are manipulated onto the sample using electrical signals, and the material needed for analysis is extracted - all on a “lab-on-a-chip” with little manual intervention. Wheeler, the Canada Research Chair in Bioanalytical Chemistry, created the prototype for this process in the Bahen Cleanroom, a facility of the Emerging Communications Technology Institute at U of T.

Wheeler’s study quantified particular amino acids that are markers of three metabolic disorders: phenylketonuria, homocystinuria, and tyrosinemia. His next steps will be to evaluate the rest of the 28 diseases that NSO screens for.

Wheeler’s innovation is indicative of the innovative tools for that IBBME researchers create. “The applications for this process go far beyond ,” Wheeler stated. “Pharmaceutical companies are moving towards dried blood spot analysis, but they’re still lacking the tools to make widespread use feasible. We’ve demonstrated that digital microfluidics could be that tool. Our system is fast, robust, precise, and compatible with automation.”

While it might be a while before the days of the dreaded needle are behind us, Wheeler’s digital method is the next step in moving to a DBS-based sampling system, said Pranesh Chakraborty, director of NSO. “This approach could save considerable costs as a result of the lower volumes of reagent required,” he affirmed. “An automated system based on this approach would also process samples faster, with higher accuracy, less risk of errors, all while freeing up time for technologists to perform other work.” Charaborty’s team provided the screening and medical perspective in this research.

A patent has been filed, and Wheeler, who also holds appointments in chemistry and Banting and Best Department of Medical Research, is currently exploring commercialization options.

Provided by University of Toronto (news : web)